[Feature]: Add notes property to ErrorInstance #10

Feature Description

Add the notes property to ErrorInstance type to store an array of note strings added via .addNote().

Problem It Solves

• The notes property is required to store notes added via .addNote()
• Enables access to error notes programmatically
• Part of the v1.1.0 enhanced developer experience

Proposed Solution

export type ErrorInstance<T extends Record<string, unknown> = Record<string, unknown>> = {
  context: Record<string, unknown> | null;
  notes: string[];
  addNote: (note: string) => ErrorInstance<T>;
};

• notes: string[] property initialized as empty array by default
• Mutation via .addNote() method
• Part of the same v1.1.0 release as .addNote()

Alternatives Considered

• Separate v1.1.1 release for just the notes property (not efficient)
• Lazy initialization (adds complexity without benefit.